The present invention relates to wheel speed sensors. It finds particular application in conjunction with high temperature wheel speed sensors and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other like applications.
Wheel speed sensors are used for detecting rotation of wheels on a vehicle. Generally, there are two (2) broad categories into which wheel speed sensors fall (i.e., those employing either active or passive sensors). Active sensors include electronic components that are typically powered by a power source associated with the vehicle. Passive sensors, on the other hand, need no outside power and usually consist of a coil surrounding a magnetic material. Both types of sensors are positioned proximate to a circular shaped element having a plurality of teeth (e.g., an exciter or tone ring), which rotates with the wheel hub.
In order to maximize the signal produced by passive sensors, precise fabrication is required so that, upon assembly, a limited clearance between a pole piece associated with the sensor and the teeth of the tone ring is maintained throughout the rotation of the wheel hub. Such precision tends to complicate the fabrication and assembly process and, furthermore, increase the cost associated with manufacturing and assembling passive sensors. Consequently, active wheel sensors, which do not require the same level of precision during fabrication or assembly, have become more desirable.
However, the electronic components included in active sensors are sensitive to higher ambient temperatures. Although active wheel speed sensors may not require as precise positioning relative to the teeth of the tone ring as passive sensors, active wheel speed sensors still must be positioned relatively close to the tone ring (e.g., on or near a spindle). Under certain conditions, this location on the vehicle tends to experience extremely high temperatures. Until now, there has been no way to maintain the temperature of the electronic components in an active sensor within a predetermined range with high temperatures around the sensor. Therefore, the performance of the electronic components and, consequently, the active sensor, have been negatively affected by high ambient temperatures.
The present invention provides a new and improved apparatus and method which addresses the above-referenced problems.